The ASTM C 185 test is described and discussed. Persistent difficulties with the test have been experienced by some users. These problems have usually taken the form of high values of the test result and have frequently caused rejection of the cement. Efforts to determine the cause of the difficulty are described. Contaminants on the sand have been strongly suspect but work to establish their nature has been inconclusive. False set of the cement may be important. Details of the test method itself have been studied. Water content, sand grading, and mixing time were shown to be most important. The work so far has failed to show clearly any reasons for the difficulties with the test.